feat(middleware): add transaction and error handling support

- Add transaction manager for multi-step database operations
- Add standardized error response middleware
- Add HTTPError type for typed errors
- Add RespondWithError and RespondWithHTTPError helpers
- Support automatic rollback on errors

internal/middleware/transaction.go

@@ -0,0 +1,53 @@
+package middleware
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/jackc/pgx/v5"
+	"github.com/jackc/pgx/v5/pgxpool"
+)
+
+// TransactionManager handles database transactions
+type TransactionManager struct {
+	pool *pgxpool.Pool
+}
+
+// NewTransactionManager creates a new transaction manager
+func NewTransactionManager(pool *pgxpool.Pool) *TransactionManager {
+	return &TransactionManager{pool: pool}
+}
+
+// WithTx runs a function within a database transaction
+// If the function returns an error, the transaction is rolled back
+// If the function succeeds, the transaction is committed
+func (tm *TransactionManager) WithTx(ctx context.Context, fn func(pgx.Tx) error) error {
+	tx, err := tm.pool.Begin(ctx)
+	if err != nil {
+		return fmt.Errorf("failed to begin transaction: %w", err)
+	}
+
+	// Ensure the transaction is handled properly
+	defer func() {
+		if p := recover(); p != nil {
+			// A panic occurred, rollback and re-panic
+			_ = tx.Rollback(ctx)
+			panic(p)
+		}
+	}()
+
+	if err := fn(tx); err != nil {
+		// Function returned error, rollback
+		if rbErr := tx.Rollback(ctx); rbErr != nil {
+			return fmt.Errorf("function error: %v, rollback error: %w", err, rbErr)
+		}
+		return err
+	}
+
+	// Success, commit
+	if err := tx.Commit(ctx); err != nil {
+		return fmt.Errorf("failed to commit transaction: %w", err)
+	}
+
+	return nil
+}